1. Field of the Invention
The present invention relates to a light source apparatus equipped with a light quantity adjusting portion for limiting light flux from a light source using an aperture blade and an endoscope apparatus equipped with the light source apparatus.
2. Description of the Related Art
Endoscopes are widely used in the medical field and the like. Endoscopes are constructed to include an elongated insertion portion. Endoscopes allow observation of organs within the body by insertion of the insertion portion into the body. When necessary, various treatments can be performed using treatment instruments introduced through a treatment instrument channel.
Endoscope apparatus including this type of endoscope guides illuminating light from a light source apparatus to illuminate a target site in the test body using a light guide or the like and obtains an endoscopic image by acquiring the return light.
The endoscope apparatus picks up the endoscopic image using an image pickup portion such as a CCD. The endoscopic image is then processed by a signal processing device and displayed on a monitor, allowing an operator to observe the target site.
In the endoscopic apparatus, light from a light source which generates a sufficient quantity of light is collected using an optical system including lenses, and guided through a light guide to the distal end of the insertion portion. Here, a light quantity adjusting portion which limits the light flux with an aperture blade is used to reduce light to a desired quantity of light by limiting light flux from the light source apparatus. For example, Japanese Patent Application Laid-Open Publication No. 2000-253307 discloses the construction shown in FIG. 1 as an aperture blade portion 120 of the light quantity adjusting portion. FIG. 1 is a plan view showing the aperture blade portion 120 seen in a light flux advancing direction. A distal end portion (screen portion) 112a of an aperture blade 112 has a circular form to allow a complete screening of a light flux 110 emitted in parallel from light source. A motor 126 is connected to an end portion side of a plate-like supporting arm 112b extending from the distal end portion 112a, and, when the motor 126 rotates, the aperture blade 112 rotates about a pivot 111 located in the supporting arm 112b. When the aperture blade 112 rotates, the area over which the light flux 110 passes the aperture blade 112, and thus the quantity of light, changes depending on the position of the distal end portion 112a. In the following description, the aperture blade 112 is said to be “closed” when moved into the light flux 110 and “open” when the aperture blade 112 is moved away from the light flux 110.
As shown in FIG. 1, the aperture blade 112 of the aperture blade portion 120 of the light quantity adjusting portion disclosed in Japanese Patent Application Laid-Open Publication No. 2000-253307 rotates in a vertical plane about the pivot 111. However, a center of gravity 130 of the aperture blade 112 is decentered with respect to the pivot 111. In other words, the aperture blade 112 has a form in which the position of the pivot 111 and the center of gravity 130 do not match.
Endoscope apparatus is generally used not only to observe the target site, but also to perform observations while the insertion portion of the endoscope is being inserted. While the insertion portion is inserted, the quantity of return light varies sharply if sites ahead of the CCD are irradiated with the constant quantity of light, making it difficult to recognize the endoscope image displayed on the monitor. Hence, light source apparatus is desired which is capable of maintaining a constant and stable brightness in the endoscope image displayed on the monitor (i.e. a constant luminance).